The present invention relates to a device for detecting and measuring variations in the height of a free level of a liquid and more particularly a liquid contained in a field pressurized enclosure, e.g. the vessel of a pressurized water nuclear reactor.
At present there are various methods which make it possible to measure the height of the free level of a liquid contained in a pressurized enclosure. A first method uses a level indicator in the form of a differential manometer, whose connecting tubes are horizontal and positioned at different heights. The main disadvantage of this device is that the upper connecting tube is continuously filled with a mixture of the liquid and its vapour, due to the partial boiling in the connecting tube, even when the level in the enclosure drops, which leads to measuring errors. A second method consists of positioning in the vicinity of the wall of the enclosure and outside the latter, a certain number of radioactive sources located at different heights and a certain number of detectors, which are generally diametrically opposite to the said sources. The comparison of the readings given by the different detectors makes it possible to determine the height of the free surface of the liquid. The latter solution requires complex equipment and therefore significantly increases the cost of such installations.